Abstract
We thank Crampin and Gao (2005, hereinafter referred to as cg) for their interest in the analysis and results of Liu et al. (2004, hereinafter referred to as ltbz). We disagree that the lines they draw through some of the data points of figure 14a of ltbz (reproduced here as Fig. 1) carry quantitative scientific information, and we maintain our assessment that the results of ltbz do not show systematic temporal evolution of anisotropy parameters that could be used to forecast impending large earthquakes in our study area. Our response to cg focuses on features involving directly the results of ltbz. We do not discuss the broader claims of cg on general scaling relations, associated with their figures 2 and 3, other than to note that they have been controversial (e.g., Aster et al. , 1990, 1991; Seher and Main, 2004). Prompted by the comment of cg, we perform a more detailed analysis of spatio-temporal variations of the time delays between fast and slow shear waves in our data. The detailed examination indicates clearly that the apparent precursory pattern identified by cg is dominated by spatial rather than temporal variations of properties. Figure 1. Observed time-delay values for the section deeper than 0.2 km versus time. Each data point is a time-delay measurement with an error given by the vertical line. The mean values and standard deviations of the measurements before and after the Chi-Chi mainshock are indicated by solid and dashed lines, respectively. The numbers near the points mark the sequential ordering of the measurements. Figure 1 is an enlarged version of figure 14a of ltbz, with sequential numbering of the data points before the 1999 Chi-Chi mainshock and several later points. The “subtle temporal changes” referred to by cg are associated with a …
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